Transcript water_in_living_orga..

1. State 4 uses of water in Living
Organisms
2. What is a ‘polar’ molecule
3. Explain why the fact that ice floats on
water is useful to living organisms
4. State 2 reasons why water is useful as
a solvent in living organisms
1. Solvent, transport medium, metabolic
reactant, temperature control
2. A positively charged end and a
negatively charged end
3. Insulation
4. Ions free to move around, organic
molecules with a polar end will
dissolve
Answers
1)
2) The alkaline properties of solution with a pH >7 are
due to hydroxide ions
3) In a water molecule, each bond between the oxygen
atom and the two hydrogen atoms are best
described as a single polar covalent bond, with a
small positive charge on the hydrogens and a small
negative charge on the oxygen
4) The acidic properties of solution with a pH <7 are
due to: hydroxonium ions
5) The dipole nature of water means that it is a good
solvent for many substances, e.g. ionic solids and
other polar molecules such as sugars and amino
acids. It is therefore readily involved in biochemical
reactions
6)
a)Clarity:
Property. Water is colourless and light
penetrates through it.
Biological importance: This property allows
photosynthesis to continue to considerable
depth. The photosynthetic region (the
euphotic zone) supports life on Earth.
b) Xylem transport:
Property. Cohesive properties and high tensile
strength.
Biological importance:
These properties allow water molecules to
stick together and move cohesively through
vessels to considerable heights (important in
water and mineral uptake from the soil).
c) Glucose transport:
Property. Water Is the universal solvent.
Biological importance: Solvent properties of
water enable materials such as glucose to be
transported around the body.
d) Thermal stability:
Property. High specific heat capacity; water
absorbs large amounts of energy for a small
rise in temperature.
Biological importance: The thermal stability of
aquatic environments allows organisms
(without thermoregulatory abilities) to
maintain stable internal temperatures despite
fluctuations in seasonal air temperatures.
e) Cooling effect of evaporation:
Property. High latent heat of vaporisation;
water absorbs large
amounts of energy before evaporating.
Biological importance: Organisms in
fluctuating environments can use sweating
and transpiration effectively in temperature
control.
7)
a) 70 × 0.4 = 28 kg muscle 28 × 0.75 = 21 kg water
b) (21/70)x100 = 30% of total body mass is water in the
muscles
8) 1 400 × 0.75 = 1 050 g water
9) Adipose tissue has a lower water content than other
tissues. Since very fat people have a higher
proportion of low-water fatty tissues compared to
thin people, the percentage of water overall will be
reduced.
10) A baby’s body has a larger ratio of tissue to bone
than an adult’s body.
11) 10% of (70 × 0.65) = 4.55 kg. So an average man can
lose 4.55 kg (4.55 l) before sweating stops.
12) Given the answer from 6a, he will have stopped
sweating by this stage and his body temperature will
start to rise. This will be serious unless he finds
some water soon; any further water loss will
certainly move him into the danger zone.
Homework
• Write an essay relating the structure of
the water molecule to its uses in living
organisms
12 Marks